1. Field of Invention
This invention relates in general to valve actuators, and in particular to an actuator override that incorporates both a manual and hydraulic override.
2. Description of Prior Art
A gate valve is a valve having a body and a bore through the body. A gate is positioned transverse to the body, and moves linearly to obstruct flow through the bore or allow flow through the bore. Gates typically have an opening that aligns with the bore to allow flow. The gate is sometimes moved, or actuated, by a valve actuator.
The valve actuator can be a pneumatic, diaphragm, piston, or hydraulic type actuator that urges a valve stem toward the valve from a first position to a second position. Urging the stem toward the valve to the second position can either open the valve or close the valve, depending on the design of the valve. A bonnet is usually connected to the valve, with the stem extending through the bonnet, and the actuator is connected to the bonnet. Actuated valves occasionally experience excessive frictional forces and require additional overriding force to fully open or close the valve. In addition, an override may be required in emergency situations in which the seals of the actuator get damaged and cannot contain pressure. In other cases, extreme conditions can cause the seals in an actuator to become damaged and lose their ability to seal, resulting in a loss of function for the actuator. Depending on the forces required to move the valve stem to the second position to open or close the valve, a manual or hydraulic override may be utilized. Operators often do not know which override will be required (manual or hydraulic); therefore, their only option is to procure, and potentially install, both pieces of equipment. It is both costly and time-consuming to carry two pieces of equipment to accomplish the same task.